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LAPACK 3.12.1
LAPACK: Linear Algebra PACKage
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subroutine slarrk | ( | integer | n, |
integer | iw, | ||
real | gl, | ||
real | gu, | ||
real, dimension( * ) | d, | ||
real, dimension( * ) | e2, | ||
real | pivmin, | ||
real | reltol, | ||
real | w, | ||
real | werr, | ||
integer | info ) |
SLARRK computes one eigenvalue of a symmetric tridiagonal matrix T to suitable accuracy.
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!> !> SLARRK computes one eigenvalue of a symmetric tridiagonal !> matrix T to suitable accuracy. This is an auxiliary code to be !> called from SSTEMR. !> !> To avoid overflow, the matrix must be scaled so that its !> largest element is no greater than overflow**(1/2) * underflow**(1/4) in absolute value, and for greatest !> accuracy, it should not be much smaller than that. !> !> See W. Kahan , Report CS41, Computer Science Dept., Stanford !> University, July 21, 1966. !>
[in] | N | !> N is INTEGER !> The order of the tridiagonal matrix T. N >= 0. !> |
[in] | IW | !> IW is INTEGER !> The index of the eigenvalues to be returned. !> |
[in] | GL | !> GL is REAL !> |
[in] | GU | !> GU is REAL !> An upper and a lower bound on the eigenvalue. !> |
[in] | D | !> D is REAL array, dimension (N) !> The n diagonal elements of the tridiagonal matrix T. !> |
[in] | E2 | !> E2 is REAL array, dimension (N-1) !> The (n-1) squared off-diagonal elements of the tridiagonal matrix T. !> |
[in] | PIVMIN | !> PIVMIN is REAL !> The minimum pivot allowed in the Sturm sequence for T. !> |
[in] | RELTOL | !> RELTOL is REAL !> The minimum relative width of an interval. When an interval !> is narrower than RELTOL times the larger (in !> magnitude) endpoint, then it is considered to be !> sufficiently small, i.e., converged. Note: this should !> always be at least radix*machine epsilon. !> |
[out] | W | !> W is REAL !> |
[out] | WERR | !> WERR is REAL !> The error bound on the corresponding eigenvalue approximation !> in W. !> |
[out] | INFO | !> INFO is INTEGER !> = 0: Eigenvalue converged !> = -1: Eigenvalue did NOT converge !> |
!> FUDGE REAL , default = 2 !> A to widen the Gershgorin intervals. !>
Definition at line 141 of file slarrk.f.